Skipped paying a fine in China? Then forget about buying an airline ticket.

Key points:

• Social credit points can be deducted for breaking the law and minor offences, like walking a dog without a leash
• Companies have lost government contacts and access to loans after being penalised for things like false advertising
• It is unclear how many people live under the social credit surveillance systems

Social credit offences including unpaid taxes and fines saw would-be air travellers blocked from buying tickets 17.5 million times last year.

Others were barred 5.5 million times from buying train tickets, according to the National Public Credit Information Centre.

In an annual report, it said 128 people were blocked from leaving China due to unpaid taxes.

The system is part of efforts by President Xi Jinping's government to use technology ranging from data processing to genetic sequencing and facial recognition to tighten control.

The Communist Party says social credit penalties and rewards will improve order in a fast-changing society after three decades of economic reform which have shaken up social structures.

Authorities have experimented with social credit across China since 2014

Points are deducted for breaking the law or, in some areas, offences as minor as walking a dog without a leash.

But human rights activists say the system is too rigid and might unfairly label people as untrustworthy without telling them they have lost status, or how it can be restored.

US Vice President Mike Pence criticised it in October as "an Orwellian system premised on controlling virtually every facet of human life".

The ruling party wanted a nationwide system by 2020 but has not yet said how it will operate.

Possible penalties include restrictions on travel, business and access to education.

No details of how many people live under social credit surveillance

Companies on the blacklist can lose government contracts or access to bank loans or be barred from issuing bonds or importing goods.

Offences penalised under social credit last year included false advertising or violating drug safety rules, the government information centre said.

Individuals were blocked 290,000 times from taking senior management jobs or acting as a company's legal representative.

Since the launch of such punishments, the system has caused 3.5 million people to "voluntarily fulfil their legal obligations," the information centre said.

It said that included 37 people who paid a total of 150 million yuan ($31.3 million) in overdue fines or confiscations.

The report gave no details of how many people live in areas with social credit systems.

Social credit is one facet of efforts by the Communists to take advantage of increased computing power, artificial intelligence and other technology to track and control the Chinese public.

The police ministry launched an initiative dubbed Golden Shield in 2000 to build a nationwide digital network to track individuals.

Human rights activists say people in Muslim and other ethnic minority areas have been compelled to give blood samples for a genetic database.

Those systems rely on foreign technology. That has prompted criticism that US and European suppliers might be enabling human rights abuses.

This week a Massachusetts-based company said it would stop selling and servicing genetic sequencers in the Muslim-majority region of Xinjiang in the northwest, following complaints they had been used for surveillance.

As many as 1 million Uighurs, Kazakhs and other Muslim minorities in Xinjiang are detained in political education camps, according to US officials and United Nations experts.

The government says the camps are vocational training centres designed to rid the region of extremism.